On long car journeys I keep the kids quiet with movies on an iPad 2 and Nexus 7 (2012). Movies are our DVDs ripped with Handbrake.

However, on both devices, especially the Nexus, the sound is no where near loud enough. No, I don't want to damage my kids' hearing but with road noise on the motorway they get very frustrated if they can't hear properly.

couple of things you could try is when ripping, make sure you rip the 2.0 stereo track if it has one as opposed to the 5.1 track as downmixing tends to have quiet issues, and then also try VLC from playback as it tends to have an audio boost (up to an extra 100%)...

Any small, rechargable Bluetooth speaker? Look out for one with the longest battery life between charges.

Better still maybe some Bluetooth gizmo that can plug into your car's hi-fi.

Or (given there are two tablets) a couple of pairs of Bluetooth wireless headphones. Then you don't have to listen to it and they can watch/listen to different things on their tablets. (Bluetooth also means they won't accidently be dragging a tablet behind them - by a headphone cable - when they jump out of the car.)

Thanks Cheeseboy that's great advice. Looks like VLC is only in beta for Android but I'll give it a go. I guess ripping 2 channel only means separate rips for NAS and tablet but worth it if I can get the volume up.

I;ve noticed this with burned movies/iPlayer etc - there is a volume limiter on the Nexus which prevents apps going louder than a certain setting, bit some apps don't notify you; if you come out of the media player and then try to increase volume, you get a notification that you are going above the recommended setting and you can say 'ok' - then the volume of the media player will go higher.

Well as it turned out I ended up buying a 2nd hand twin in car DVD player on the auction site for £40. At least the kids can then watch the same thing, adjust the volume themsleves and won't keep turning off or pausing the film by touching the screen.